Device for forming a pyrolytic coating

ABSTRACT

A device for the formation, by pyrolysis, of a coating composed of metal or a metal compound on a face of a hot glass substrate which is in motion by bringing the face into contact with a gaseous reagent, includes a vault; support device for conveying the hot glass substrate along a path through a coating chamber defined between the vault and the face; device for supplying and distributing gaseous reagent to the coating chamber as a flow; and device for discharging exhaust gas from the coating chamber. The device for supplying and distributing gaseous reagent includes an ejection nozzle having defined therein a slot which opens directly into the coating chamber and has longitudinal internal walls which are substantially parallel to each other. The ejection nozzle has longitudinal internal walls which define a continuous convergent path which terminates at and communicates with the slot and which has an angle of convergence (α), thereby causing the flow of gaseous reagent to conform to the slot. The angle of convergence (α) of the convergent path ranges from 4° to 14° at any point.

This Application is a continuation of Application Ser. No. 08/552,048filed Nov. 2, 1995, which is a continuation of Application Ser. No.08/178,906 filed Jan. 6, 1994 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for the formation, bypyrolysis, of a coating of metal or metal compound on one face of amoving hot glass substrate by bringing said face into contact with agaseous reagent, comprising support means for conveying the substratethrough a coating chamber, means for supplying and distributing reagentgas to the coating chamber and means for discharging exhaust gas fromthe coating chamber, and a method for forming a coating of metal ormetal compound on a moving hot glass substrate by pyrolysis of a reagentin the gaseous phase.

The coating of metal or metal compound formed on a hot glass substrateby pyrolysis is used for modifying the apparent colour of the glassand/or presenting other properties required vis-a-vis incidentradiation, for example the property of reflecting infrared. A singlecoating on the glass substrate may be used for these purposes, or amulti-layer coating. Examples would be coatings of tin oxide SnO₂, tinoxide SnO₂ doped with fluorine, titanium dioxide TiO₂, titanium nitrideTiN, silicon nitride Si₃ N₄, silica SiO₂ or SiO_(x), alumina Al₂ O₃,vanadium pentoxide V₂ O₅ or tungsten oxide WO₃ or molybdenum oxide MoO₃,and in general oxides, sulphides, nitrides or carbides and a layering oftwo or more of these coatings.

The coating can be formed on a sheet of glass which moves in a tunneloven or on a glass ribbon during formation, whilst it is still hot. Thecoating can be formed inside the lehr which follows the glass ribbonforming device or inside the float tank on the top face of the glassribbon whilst the latter is floating on a bath of molten tin.

2. Description of the Related Art

To form the coating, the substrate is brought into contact, in a coatingchamber, with a gaseous medium comprising one or more substances in thegaseous phase. The coating chamber is fed with a reagent gas through oneor more slots, the length of which is at least equal to the width to becoated, fed through one or more ejection nozzles. Depending on the typeof coating to be formed and the reactivity of the substances used, ifseveral substances have to be used, these are distributed either in theform of a mixture by a single ejection nozzle in the coating chamber viaa slot, or separately by several ejection nozzles via separate slots.

Methods and devices for forming such a coating are described for examplein French patent No 2 348 166 (BFG Glassgroup) or in French patentapplication No 2 648 453 A1 (Glaverbel). These methods and devices leadto the formation of particularly strong coatings with advantageousoptical properties.

However, it is difficult by this technique to form coatings which areuniform across the width of the substrate, when the substrate is a largesurface, such as the surface of a ribbon of float glass moving at arelatively high speed. A lack of uniformity is then found in thedistribution of this coating over the entire surface of the substrate tobe coated, which results for example in alternating streaks, the visualappearance of which, mainly in reflection, is different either in colouror in the degree of reflection.

SUMMARY OF THE INVENTION

The object of the present invention is to improve the uniformity ofdeposition of a coating effected by pyrolysis starting from one or moresubstances in the gaseous phase.

We have found that this and other advantageous objectives can beachieved when the means for distributing reagent gas to the coatingchamber includes an ejection nozzle having a slot opening directly intothe coating chamber, the longitudinal internal walls of the slot beingsubstantially parallel to each other, the slot extending transverse tothe path of the substrate, the length of said slot being at leastsubstantially equal to the coating width of the substrate (that is, tothe width of that part of the substrate which it is desired to becoated), and the internal walls of the ejection nozzle define acontinuous convergent path, to cause the flow of reagent gas to conformto the dimension of the opening of the slot, the angle of convergence ofsaid convergent path not exceeding a specified limit at any point.

Thus, according to the invention, there is provided a device for theformation, by pyrolysis, of a coating of metal or metal compound on oneface of a moving hot glass substrate by bringing said face into contactwith a gaseous reagent, comprising support means for conveying thesubstrate through a coating chamber, means for supplying anddistributing reagent gas to the coating chamber and means fordischarging exhaust gas from the coating chamber, characterised in thatthe means for distributing reagent gas to the coating chamber includesan ejection nozzle having a slot opening directly into the coatingchamber, the longitudinal internal walls of the slot being substantiallyparallel to each other, the slot extending transverse to the path of thesubstrate, the length of said slot being at least substantially equal tothe coating width of the substrate, and in that the internal walls ofthe ejection nozzle define a continuous convergent path, to cause theflow of reagent gas to conform to the dimension of the opening of theslot, the angle of convergence (α) of said convergent path not exceeding14° at any point.

It was found that, by complying with this condition with respect to theangle of convergence of the internal walls of the erection nozzle, auniform flow of reagent gas is conformed to the dimension of the openingof the slot and the distribution of the coating over the surface of thesubstrate was more uniform and the streaks could be avoided more easily.It is believed that this advantage could be due to the fact that thisangle limit assists the flow of the reagent gas in the nozzle in theform of a quasi-laminar flow. It is surprising that a laminar flow in anejection nozzle assists the formation of a uniform coating. In fact,firstly, at this point the reagent gas is still not in contact with thesubstrate. Secondly, mainly when several reagents are necessary to formthe layer, turbulence movements are created in the ducts conveying gasin order to assist an intimate mixture of the gaseous reagent for thepurpose of improving its homogeneity so as to achieve uniform treatment.

European patent specification EP-A-365240 (Pilkington PLC) describes anapparatus for depositing a coating onto the surface of a moving ribbonof hot glass. The apparatus includes a nozzle in the form of aconverging fantail distributor which directs reactant gas to a narrowslot extending across the width of the glass ribbon to be coated. Thereactant gas passes from the narrow slot through a gas flow restrictorbefore entering the coating chamber. In contrast to this arrangement,the present invention provides that the slot opens directly into thecoating chamber. While the arrangement described in EP 365240 maycontribute to the formation of a coating of which the general appearanceis relatively uniform across the width of the glass ribbon when examinedin a macroscopic manner, a streak-free coating where the uniformity mayalso be confirmed from one small portion to the next small portion ofthe width of the coating can be facilitated by the provisions of thepresent invention.

The continuous convergence path preferably has an angle of convergencewhich does not exceed 9° at any point. This feature allows thedeposition of a more uniform coating. In order to avoid the need forexcessive space requirements, the angle of convergence is at least 4° atany point. This feature facilitates the unification of flow across thewidth of the slot, thanks to the increase in pressure caused by asufficient degree of convergence. Ideally, the longitudinal walls of theconvergent portion of the ejection nozzle form a truncated dihedron, thedihedral angle of which is said angle of convergence. This is a simplemanner by which a regular, continuously convergent flow path may beachieved.

In one embodiment of the invention, the distribution means comprises atleast one spreading device, for spreading out the flow of gaseousreagent, which defines a divergent path for broadening out the flow ofreagent gas from its dimension at the exit from the supply means to adimension equal to at least part of the length of the slot. Thisconstruction favours the effective distribution of the gas feed to thenozzle. The internal walls of the spreading device or devices preferablydefine an angle of divergence which does not exceed 14°, most preferablynot more than 9°, at any point, to achieve a more uniform feed to thenozzle.

We have found that the low divergence prevents the gas flow being shedfrom the walls of the spreading device, thus preventing the formation ofvortical movements. Whilst avoiding the shedding of the gas flow fromthe walls of the spreading device, compliance with this condition alsoreduces the risk of formation of areas in which the flow of reagent gasis almost stationary. In the case of a highly reactive gas or one whichis easily decomposable under the action of heat, this could lead to theformation of liquid or solid deposits liable to form defects in thecoating.

Preferably, the spreading devices and the nozzle constitute a singlecomponent, the spreading devices supplying the nozzle with reagent gas.This avoids the need for transition zones between the spreading devicesand the nozzle which might cause a disturbance in the flow of thereactive gas.

Preferably, each of the longitudinal walls of the ejection nozzle formsa single piece with the corresponding wall of the spreading device,which is cut substantially in the form of truncated isosceles trianglesto form the spreading devices.

In a preferred embodiment of the invention, the inlet cross-section ofeach spreading device is circular or rectangular (such as substantiallysquare) and the outlet cross-section is an elongate rectangle which fitsat least part of the inlet cross-section of the ejection nozzle.

In contrast to previously proposed arrangements, such as that shown inFIG. 12 of U.S. Pat. No. 5,122,394 (Lindner/Atochem North America Inc.)in which two reactive gas supply systems are linked together for coatinga substrate of large width, the present invention preferably providesthat the distribution means comprise several spreading devices which areconnected to each other, in order to distribute the gaseous reagentsover the entire length of the nozzle, it being an essential feature ofthe present invention that the slot extends over the entire coatingwidth of the substrate. The advantage of this feature is the uniformfeeding of reactive gas to a slot of some length. The several spreadingdevices are preferably connected to each other at a distance of at least10 cm, and preferably at least 15 cm, from the said slot. This distanceavoids that the junctions between adjacent feeds might result in a lossof uniformity of the coating.

The nozzle ends in a slot which opens directly into the coating chamber.The slot differs from the ejection nozzle and the spreading devices byhaving parallel walls. The flow of reactive gas through the slot isthought to be non-laminar, the advantage of the invention in terms ofthe production of uniform coatings being derived from the quasi-laminarflow through the ejection nozzle. While the slot may be in line with theejection nozzle, the use of a slot disposed at an angle to the ejectionnozzle, or the use of a slot providing a non-straight gas flow path, isalso possible. In order to help maintain the parallel disposition of thewalls of the slot, struts may be positioned at spaced intervals,connecting opposite walls of the slot together. In order to reduce theeffect of these struts upon the uniformity of gas flow through the slot,the number of struts should be kept to a minimum and their profileshould be such as to present low resistance to the flow of gas. Strutshaving a cross-section of "waterdroplet" shape have been found to besuitable for this purpose.

The longitudinal internal walls of the slot preferably form, with theplane of movement of the substrate, an angle of between 20° and 40°.Preferably, the slot is integral with the nozzle itself.

The slot should have a gas flow path of such a length which issufficient to form a flat jet of reactive gas entering the coatingchamber, depending upon the gas flow rate. We have found that at a gasflow rate of 1 m³ /cm slot width/hr, a gas flow path in the slot of from40 mm to 200 mm is suitable. The spacing between the slot wallspreferably has a dimension which is at least 6 times smaller than thegas flow path in the slot.

The axial plane of the nozzle may be inclined at an angle of between 20°and 40° to the plane of movement of the substrate. Preferably, the axialplane of the nozzle is substantially perpendicular to the plane ofmovement of the substrate to avoid overcrowding.

It is difficult to distribute vapour uniformly over large distances. Todeposit a uniform coating over the entire width of a glass ribbon (e.g.approximately 3 m) it would obviously be possible to locate severalvapour distribution slots, each fairly short in length, for example 70cm, side by side so as to occupy in this way the entire width of theglass. This however poses a major difficulty since the joining of thegas flows coming from the different slots causes defects in uniformityin the coating which is deposited on the glass. This problem is resolvedin embodiments of the present invention by the use of a single slotextending over the entire coating width of the glass.

The invention also extends to a method for forming a coating of metal ormetal compound on a moving hot glass substrate by pyrolysis of a reagentin the gaseous phase, characterised in that a gas flow is formed bysupplying an ejection nozzle having a slot opening directly into thecoating chamber, the longitudinal internal walls of the slot beingsubstantially parallel to each other and the slot extending over atleast substantially the entire coating width of the substrate, with agaseous medium which comprises one or more substances in the gaseousphase, a substance or substances which undergo a chemical reaction or adecomposition to form the said metal or said metal compound on thesubstrate, and the substrate is brought into contact with the said gasflow ejected through the said slot, and in that the angle of convergence(α) of the gas flow is, at any point along its path inside the ejectionnozzle, equal to or less than 14°.

Two types of installation have been developed, allowing the continuousin-line formation of a coating by the pyrolysis of a reagent or reagentsin the vapour phase (CVD) on a ribbon of hot glass manufactured by thefloat process. The two types of installation for depositing a coatingmay be described as an asymmetrical installation and a symmetricalinstallation.

An asymmetrical installation has already been described in patentsspecifications GB 1524326 and GB 2033374 (BFG Glassgroup), whilst asymmetrical installation was described in patent specifications GB2234264 and GB 2247691 (Glaverbel).

The installations according to the invention include better and improvedfeatures compared with those described previously. Both types ofinstallation can be placed above the glass ribbon after it emerges fromthe float tank or over the glass whilst it is still in the float tank.

They enable substantially the entire width of the glass ribbon, e.g.approximately 3.20 m, to be covered.

These installations may be removable. They can therefore be put inposition to produce coated glass and withdrawn whenever necessary.

A system for the deposition of a layer in a float tank may include meansto ensure accurate geometry and functioning even at the hightemperatures which prevail in a float tank. Thus, the coating depositingdevice may be coupled to a bogie carrying a plurality of rollers adaptedto engage fixed guide beams. In particular the bogie may run by means offour rollers on two guide beams (I.P.N. 350). These beams may be ribbedwith complementary flats which have a double purpose: increasing themoment of inertia, both vertical and horizontal, and also constitutingchannels in which water circulation may be provided, which makes itpossible to maintain an identical geometry of the device both at ambienttemperature and at high temperature. The bogie may be guided by at leastone, such as two U-shaped rollers which run on a first guide beam orrail, whilst lateral movements may be enabled by at least one, such astwo cylindrical rollers running on a second guide beam for compensatingfor any transverse undulations in the running tracks.

Preferably, the device further comprises means to adjust the height ofthe coating chamber above the glass substrate. Thus, rams may beprovided to enable the distance between the glass and the roof of thecoating chamber to be adjusted to a distance which is generally lessthan 50 mm (preferably between 3 and 30 mm).

The float tank may be sealed, at the point where the device passes, bymeans of a bellows system.

The device may further include means for trapping stray deposits in thecoating chamber, for example one or more metal bars disposed below thevault of the coating chamber. Such a device is the subject matter of ourcopending application which claims priority from British PatentApplication No. 93 00 400.0 dated Jan. 11, 1993, filed on even dateherewith, entitled "A DEVICE AND METHOD FOR FORMING A COATING BYPYROLYSIS" which copending application corresponds to U.S. applicationSer. No. 08/952,048 filed Nov. 2, 1995, now U.S. Pat. No. 5,709,726,which is a continuation of U.S. application Ser. No. 08/178,844 filedJan. 6, 1994, now abandoned.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be illustrated by reference to the accompanyingdrawings in which:

FIG. 1 shows in vertical cross-section an asymmetrical installationaccording to the invention;

FIG. 1A is a cross-section taken along the line I--I in FIG. 1;

FIG. 2 shows a cross-section similar to FIG. 1A, of an alternativeasymmetrical installation according to the invention, suitable forcoating a wider glass substrate;

FIG. 3 shows a detail of part of the installation shown in FIG. 2,viewed in the direction III in FIG. 2;

FIG. 4 shows in vertical cross-section a symmetrical installationaccording to the invention;

FIG. 5 shows a detail of part of the installation shown in FIG. 4;

FIG. 6 shows detail of the same part of the installation as shown inFIG. 5, viewed in the direction VI in FIG. 5;

FIG. 7 shows an alternative embodiment of part of the installation shownin FIG. 4;

FIG. 8 shows detail of the same part of the installation as shown inFIG. 7, viewed in the direction VIII in FIG. 7;

FIG. 9 shows, in enlarged section, an alternative construction for partof an installation according to the invention; and

FIG. 10 shows, in enlarged section, a further alternative constructionfor part of an installation according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 1A show the whole of an asymmetrical installation whichcomprises three main parts:

(i) two vaporised or gaseous reagent ejection nozzles 10, each having aheight of 85 cm and incorporating a slot 12a, 12b, each slot having agas flow path of 15 cm, an opening dimension of 8 mm and a spacingbetween the slot walls of 4 mm;

(ii) a coating chamber 14, consisting of a flat vault defining a channelopen towards the bottom, above the glass 16; and

(iii) a slot 18 for extracting the used vapours.

The ribbon of glass 16 is supported by rollers 20 and driven in thedirection indicated by the arrow A.

The flow of the vapours in the coating chamber 14 along the glass 16 ismainly controlled by suction.

When hot reagents have to be brought into contact with the glass 16 at apoint located outside the float tank, the whole installation ispreferably insulated.

The number of successive reagent supply slots 12a,b depends on thenature of the coating to be formed. These slots 12a,b are inclinedtowards the coating chamber 14.

Maintaining a uniform flow rate of vapour or gas across the width of thesubstrate is also facilitated by the parallelism of the walls 24 of theinlet slots 12a,b and extraction slot 18.

This device can be placed over the glass 16 so that the reagents flow inthe direction of movement A of the ribbon or in the opposite direction.

The supply means for the gaseous reactants are constituted by a deliverypipe 22 connected to an adapter 26 which leads into the nozzle 10. Thelongitudinal walls 34 of the convergent portion of the ejection nozzle10 form a truncated dihedron 11, the dihedral angle of which, or angleof convergence (α) is 9°, this angle of convergence (α) being determinedin the transverse sense of the slot 12a,b.

The low convergence angle (α) causes a smooth redistribution of thedischarge gas stream pressure in a laminar manner, without sudden localvariations in pressure. This contributes to the uniformity of thecoating.

The vault or roof 38 of the coating chamber 14 is 20 mm from the glass16. The length of the coating chamber 14 is chosen so that the reagentremains in contact with the glass 16 for 6 to 10 seconds. In practice,the length of the coating chamber 14 is chosen once and for all,according to the most usual speed of travel of the glass 16--i.e. about14 m/min for 4 mm glass--and the concentration of reagent is adjustedwhenever necessary according to the nature and thickness of the coatingto be obtained.

The installation is sealed by means of carbon fibre joints when theinstallation is situated in a float tank or by REFRASIL (Trade Mark) orCERAFELT (Trade Mark) skirts, possibly impregnated with boron carbide,when the installation is situated out of a float tank. REFRASIL andCERAFELT are high temperature insulating cloths. REFRASIL is a textilemade of filaments of amorphous silica. CERAFELT is a felt made ofrefactory fibers of a formulation including alumina, silica, andzirconia. The installation may also be sealed, at least upstream, by thepresence of a gas joint (cfr.: references 244 in FIG. 4) which preventsentry of ambient atmosphere in the coating chamber.

To prevent fouling of the coating chamber 14 by stray deposits which mayfall on the glass 16 and create defects in the coating formed on it, theinstallation includes a system for trapping stray deposits, as describedin our co-pending application filed on even date herewith referred toabove. Metal bars 40, made from stainless steel, are disposed underneaththe vault of the coating chamber 14. These bars preferentially collectthe solid material which forms above the glass 16 and divert the gascurrents away from the vault, which remains clean. The bars movetransversely as the glass 16 travels, thus making it possible towithdraw the fouled part progressively and replace it with a clean part.Instead of transverse bars, it is possible to use a cable which moves ina closed circuit. This device is particularly useful in installationsusing hot reagents.

The installation is formed from annealed metal pieces fixed to eachother by bolts rather than welding to avoid thermal distortion.

In the embodiment shown in FIGS. 2 and 3, there is provided severalfeeds disposed along a slot 112. The special geometry for the feedsdistributes the reactive vapour homogeneously along a single slot 112occupying the entire coating width of a glass ribbon (almost 3 m long)to supply the slot evenly with reactive vapours.

The supply means for the gaseous reactants are constituted by sixcircular delivery pipes 122 connected to six pyramids 128 which leadinto the slot 112. The inlet cross-section 129 of each pyramid 128 is 10cm by 20 cm rectangular. To match the outlet cross-section of thedelivery pipes 122 there are provided adapters 126. The outletcross-section of each pyramid 128, indicated by the imaginary line 130,is an elongate rectangle which fits one part of the inlet cross-sectionof the ejection nozzle 110, indicated by the imaginary line 132.

The six pyramids 128 constitute spreading devices the diverging internalwalls 136 of which define between them an angle of divergence (β) of14°, this angle of divergence (β) being determined in the longitudinalsense of the slot 112. The spreading devices together with the adapters126 broaden out the flow of reagent gas from its dimension at the exitfrom the delivery pipes 122 to a dimension equal to the length of theslot 112. The pyramids 128 and the adapters 126 together constitute thedistribution means leading from the delivery pipes 122 to the ejectionnozzle 110.

The longitudinal walls 134 (see FIG. 3) of the convergent portion of theejection nozzle 110 and of the six pyramids 128 form a truncateddihedron 111, the dihedral angle of which, or angle of convergence (α)is 9°, this angle of convergence (α) being determined in the transversesense of the slot 112. Each longitudinal wall 134 of the ejection nozzleforms a single piece with the corresponding walls of the six pyramids,which is cut substantially in the form of truncated isosceles trianglesto form the six pyramids.

The low divergence and convergence angles α, β enable a stream of gas toflow without separation from the walls and therefore without anyvortices and favour the equalisation of pressure.

The feed device makes it possible to change from several delivery pipes122 with a circular cross section to a single rectangular cross sectionas possessed by the slot 112.

This device has considerable advantages since it makes it possible toobtain a homogeneous distribution of vapour without introducing anyunnecessary head loss or areas of stagnation where corrosion of thematerials of the device could occur.

The height of the dihedron 111 providing connection of the six pyramidsto the slot 112 (of the order of 20 cm) is chosen so as to obtain a goodcompromise between producing uniformity of flow and the size of thedevice. The height of the spreading devices, i.e. of the pyramids 128,is 60 cm.

The delivery of gas through each delivery pipe 122 can be controlledindividually by means of valves 123, which proves useful for controllingthe transverse uniformity of thickness of the deposit. In this way it ispossible to take account of and compensate for the existence oftransverse temperature gradients between the centre and edges of theglass ribbon.

Maintaining a uniform flow rate of vapour or gas across the width of thesubstrate is also facilitated by the parallelism of the walls 124 of theinlet slots 112. This parallelism is maintained by virtue of thepresence of struts 125 with a profile in the shape of a drop of water,positioned with its widest part towards the upstream of the gas current.The choice of this geometry reduces or eliminates the formation of atrail of different pressure downstream of the strut. A strut height of29 mm and a greatest width of 12 mm has been found to be suitable. It ispreferable that the struts 125 are positioned sufficiently away from theexit of the slot to avoid the formation of streaks on the coating. Bypreference this distance is at least 7 cm. On the other hand, the struts125 should not be placed too far from the exit of the slot otherwisethey may not provide sufficient rigidity to maintain a constant spacingalong the length of the slot. Preferably this distance is less than 15cm, advantageously between 8 and 12 cm, such as 10 cm. Furthermore, aspacing between the struts of about 25 cm is used (exaggerated in theFigures for the sake of clarity).

The introduction of the reagent into its carrier gas takes place at atubular pipe 122 at a point situated before its connection to theadapter 126. This pipe is fitted with venturis 127a, 127b. At the neckof a first venturi 127a, tin chloride SnCl₄ is atomised, for example,and this is entrained in the hot nitrogen, and the carrier gas/vapourmixture is completed by passing through a second venturi 127b. The sameapplies to the introduction of the water vapour into another pipe.

When the installation is used for depositing a coating on a glass ribbonwhen the latter has left the float tank, the complete machine can beplaced on a chassis which includes the heating elements for the carriergases and the pipework for connecting the hot gases to the adapters 126feeding the slots 112.

If it is desired to reduce the vertical dimensions of the installation,the vertical pyramid system is replaced with pyramids 128 inclined tothe plane of the substrate in the same plane as the slots 12a,b in FIG.1.

The variation shown in FIG. 9 may be adopted in the installation of FIG.1 or FIG. 3. In this variation, the nozzle 410 has a major upperconvergent portion 460 having an axial plane extending substantiallyperpendicular to the surface of the substrate to be coated and a minorlower convergent portion 462, the axial plane of which is inclined tothe coating surface, the walls 464 of the lower convergent portion beingintegral and continuous with the parallel walls 424 of the slot 412.Struts 425 are disposed in the lower convergent portion 462 of thenozzle 410 in order to maintain the parallel disposition of the walls424 across the width of, the device.

The variation shown in FIG. 10 may be adapted to the installation ofFIG. 1 or FIG. 3. In this variation, an ejection nozzle 510 has a slot512, the axial plane of which extends in a direction inclined to thecoating surface. The slot 512 is formed by parallel side walls 524, eachof which includes a step 565 which defines an upper slot portion 566 anda lower slot portion 567. In the upper slot portion 566, the walls 524are spaced further apart than in the lower slot portion 567. Struts 525are disposed in the upper slot portion 566 of the slot 512 in order tomaintain the parallel disposition of the walls 524 across the width ofthe device.

Examples--Asymmetrical

The following Examples illustrate the use of an asymmetricalinstallation such as described in connection with FIGS. 1, 1A, 2 and 3.

The installation enables one to deposit, for example, coatings of tinoxide SnO₂, tin oxide SnO₂ doped with fluorine, titanium dioxide TiO₂,titanium nitride TiN, silicon nitride Si₃ N₄ and, in general terms,oxides, sulphides, nitrides or carbides.

To form coatings of tin oxide SnO₂ or titanium dioxide TiO₂, twosuccessive slots 112 are used. The reagent carrying the metal (Sn or Ti)(fed in at the first slot 112a) is a tetrachloride, liquid at ambienttemperature, vaporised in a current of anhydrous carrier nitrogen gas atabout 600° C. Vaporisation is facilitated by the atomisation of thesereagents in the carrier gas.

To produce the oxide, the molecules of tetrachloride are brought intothe presence of water vapour conducted to the second slot 112b. Thewater vapour is superheated to about 600° C., and is also injected intoa carrier gas, which is air heated to about 600° C. SnO₂ may be formedfor example using the proportions of SnCl₄ and H₂ O given in Britishpatent specification GB 2026454 (Glaverbel).

In the case of the formation of conductive tin oxide SnO₂, the dopant isfluorine: HF is added to the water vapour. The HF partial pressure ispHF=0.2 pSnCl₄. Another dopant can also be introduced: liquid antimonychloride SbCl₅ which is directly mixed with the tin chloride SnCl₄, withwhich it is miscible in any proportions. The presence of the antimonychloride SbCl₅, makes it possible to colour the coating of tin oxideSnO₂, which can then absorb (and reflect) some of the near solarinfrared radiation.

The flow rate of gas (carrier gas+reagent) in each slot 112 is 1 m³ /cmof slot/hr, at the operating temperature.

To deposit coatings of tin oxide SnO₂ or titanium dioxide TiO₂, INCONEL600 or optionally an even more refractory alloy (HASTELLOY) is chosenfor the parts of the device which are in contact with tin chloride SnCl₄or titanium chloride TiCl₄ and MONEL 400 for the water vapour and HFslot. INCONEL identifies nickel alloys and, for example, INCONEL 600 iscomposed mainly of 75% Ni, 15.5% Cr, and 8% Fe. HASTELLOY is a nickelalloy resistant to oxidizing conditions at high temperature and, forexample, HASETOLLY C is composed of 54% Ni, 17% Mo, 15% Cr, 5% Fe, and4% w. MONEL identifies nickel alloys and, for example, MONEL 400 iscomposed of 65% Ni, 32% Cu, 1.5% Fe, and 1% Mn.

The layer which is formed is uniform, both when examined in amacroscopic manner over the whole of the width of the coated substrate,and when small neighbouring zones are examined. The coating isstreak-free.

The symmetrical installation shown in FIGS. 4, 5 & 6 includes a centralreagent injection slot 212, on each side of which is a coating chamber214a, 214b consisting of a channel connected to a suction slot 218a,218b. This symmetrical installation occupies substantially the entirewidth of the glass 16.

Several features of the device are similar to those described withrespect to the asymmetrical installation shown in FIGS. 1, 1A, 2 and 3:injecting reagent into the carrier gas by means of venturis, andmaintaining the parallelism of the injection and suction slots by meansof "water droplet" struts 225.

The symmetrical installation, shown in FIG. 4, is 3 m long, and isdesigned to have a deflection which does not exceed 1 mm, even in ahigh-temperature environment.

The installation is suited to the deposition of a coating from reagentswhich have to be kept cold until the moment when they make contact withthe hot glass 16. The device includes only a single reagent feed slot212. It is possible to introduce through this slot 212 a mixture ofseveral reagents which will react with each other only when thetemperature is sufficiently high, and therefore on the glass 16. Theinstallation is constructed from aluminium and provided with coolingducts 242.

This assembly is located at a height of less than 12 mm above the glass16, for example 4 mm. The presence of this cooled device interferes withthe temperature of the glass 16 to only a small extent or not at all,since the coating chamber 214a,b consists of a polished aluminium vaultwith a very low emissivity, which fulfils the role of a thermal mirror.

The installation is airtight because of the presence of gas joints 244upstream and downstream which prevent any exchange between the ambientatmosphere and the coating chamber 214a,b. Lateral screens are alsoprovided, supplemented by suction and a gas joint, in particular when itis not possible to use self-lubricating mechanical joints (graphite,boron carbide) (in the case of oxidised layers).

To enable the deposition of a layer on a glass substrate in a floattank, one ideally needs to include means to ensure accurate geometry andfunctioning even at the high temperatures which prevail in a float tank.As shown in FIG. 4, the coating depositing device is fixed to a bogie247 carrying rollers adapted to engage fixed guide beams. In particularthe bogie 247 runs by means of four rollers on two guide beams 249, 251(I.P.N. 350). The bogie 247 is guided by one pair of rollers 248 havinga U-shaped profile, which run on a first guide beam or rail 249, whilstlateral movements may be enabled by one pair of cylindrical rollers 250running on a second guide beam 251 for compensating for any transverseundulations in the running tracks. These beams are ribbed withcomplementary flats which have a double purpose: to increase the momentof inertia, both vertical and horizontal, and also to constitutechannels in which water circulation may be provided, which makes itpossible to maintain an identical geometry of the device both at ambienttemperature and at high temperature.

The injection slot 212 of the nozzle 210 is provided with fiveadjustable feeds 246 conveying the vapour into an injection nozzle inthe form of a dihedron 211 terminating in the slot 212, the dihedralangle or angle of convergence (α) being 9°. A greater number ofadjustable feeds, such as 16, may alternatively be provided. The heightof the slot 210 is 20 cm.

The slot 312 may be curved as shown in FIGS. 7 and 8. While this designmay complicate the installation, it can offer the advantage of a smallerspace requirement with respect to height, if the walls 324 of the slot312 are positioned horizontally and its feed dihedron vertically.

Examples--Symmetrical

The following Examples illustrate the use of a symmetrical installationsuch as described in connection with FIG. 4.

The installation enables one to deposit coatings of silica SiO₂ orSiO_(x) from silane SiH₄ and oxygen in accordance with the descriptionsin British patent specifications GB 2234264 and GB 2247691, referred toabove.

A similar installation can also be used to form a coating of alumina Al₂O₃ from aluminium acetylacetonate vapour. In this case the material incontact with the reagent vapour will be stainless steel.

This same type of installation can also be used for depositing ametallic coating from a metal carbonyl.

Such an installation can be converted to use reagents which cannot comeinto contact with each other during their conveyance to the glass 16. Inthis case, two reagent feed dihedrons are placed side by side, eachterminating in an inclined slot, the plane of inclination of whichconverges towards the plane of inclination of the other slot. Thisdevice should ideally not be cooled.

By way of example, several successive installations may be used fordepositing coatings on glass whilst the latter is in the float tank;first of all silica SiO₂, and then vanadium pentoxide V₂ O₅ or tungstenoxide WO₃ or molybdenum oxide MoO₃, in which sodium in the atomic statewill be diffused, to transform this oxide into vanadium, tungsten ormolybdenum bronze, and finally an tin oxide SnO₂ barrier will besuperimposed. The tin oxide SnO₂ barrier can optionally also bedeposited on the ribbon just after it emerges from the float tank. Suchdeposits have an electrical conductivity (bronze) such that they arehalfway between precious metal and heavily-doped semiconductors. Thus aglass is obtained bearing a coating which is optically very selectivewith a metallic appearance in reflection and a very low solar factor.

The layer which is formed is uniform, both when examined in amacroscopic manner over the whole of the width of the coated substrate,and when small neighbouring zones are examined. The coating isstreak-free.

What is claimed is:
 1. A device for the formation, by pyrolysis, of acoating having a coating width and being composed of metal or a metalcompound on a face of a hot glass substrate which is in motion bybringing the face into contact with a gaseous reagent, the devicecomprising:a vault; support means for conveying the hot glass substratealong a path through a coating chamber defined between the vault and theface of the hot glass substrate; means for supplying and distributinggaseous reagent to the coating chamber as a flow; and means fordischarging exhaust gas from the coating chamber,wherein the means forsupplying and distributing gaseous reagent to the coating chamberincludes an ejection nozzle having defined therein a slot which opensdirectly into the coating chamber, the slot having longitudinal internalwalls which are substantially parallel to each other, the slot extendingtransverse to the path of the hot glass substrate, and the slot having alength which is at least substantially equal to the coating width of thecoating, and wherein the ejection nozzle has longitudinal internal wallswhich define a continuous convergent path which terminates at andcommunicates with the slot and which has an angle of convergence (α),thereby causing the flow of gaseous reagent to conform to the slot, theangle of convergence (α) of the convergent path ranging from 4° to 14°at any point.
 2. The device according to claim 1, wherein the means forsupplying and distributing gaseous reagent to the coating chambercomprises a plurality of delivery means and a plurality of spreadingdevices for spreading out the flow of gaseous reagent, wherein theplurality of spreading devices have respective longitudinal walls anddefine respective divergent paths for broadening out the flow of gaseousreagent from its dimension as it exits respective ones of the pluralityof delivery means to a dimension equal to at least part of the length ofthe slot, and wherein the plurality of spreading devices have respectivepyramidal forms each including a section that is substantially anisosceles triangle and are juxtaposed to each other at their respectivebases in order to distribute the gaseous reagent from the plurality ofdelivery means over the entire length of the nozzle at a distance of atleast 10 cm from the slot.
 3. A method for forming a coating having acoating width and being composed of metal or a metal compound on a hotglass substrate which is in motion, by pyrolysis of a reagent in thegaseous phase, the method comprising:a. providing a device for forming acoating, which device includes an ejection nozzle; b. forming a gas flowof a gaseous medium by supplying the gaseous medium to the ejectionnozzle,wherein the ejection nozzle has a slot which ejects the gaseousmedium, which opens directly into a coating chamber defined between avault and the hot glass substrate, which has longitudinal internal wallswhich are substantially parallel to each other; and which extends overthe hot glass substrate substantially over at least the coating width ofthe hot glass substrate to be coated, and wherein the gaseous medium iscomprised of at least one substance in the gaseous phase which undergoesone of a chemical reaction or a decomposition to form the metal or themetal compound on the hot glass substrate; and c. bringing the hot glasssubstrate into contact with the gaseous medium of the gas flow ejectedthrough the slot into the coating chamber,wherein the ejection nozzlehas longitudinal internal walls which define a continuous convergentpath which terminates at and communicates with the slot and which has anangle of convergence (α) which ranges from 4° to 14°, thereby causingthe gas flow to conform to the slot, wherein the gas flow has an angleof convergence; and wherein the angle of convergence of the gas flowranges, at any point along its path inside the ejection nozzle, from 4°to 14°.
 4. The device according to claim 1, wherein the longitudinalinternal walls of the continuous convergent path of the ejection nozzleform a truncated dihedron having a dihedral angle which is the angle ofconvergence (α).
 5. The device according to claim 2, wherein the slothas a length and a width, and wherein the plurality of spreading deviceshave respective internal walls which define the angle of convergence (α)and an angle of divergence (β) which does not exceed 14° at any point,the angle of divergence (β) being determined based on the length of theslot, and the angle of convergence (α) being determined based on thewidth of the slot.
 6. The device according to claim 5, wherein the angleof divergence (β) does not exceed 9° at any point.
 7. The deviceaccording to claim 2, wherein the plurality of spreading devices and theejection nozzle are joined together as a continuous component, theplurality of spreading devices supplying the ejection nozzle withgaseous reagent.
 8. The device according to claim 7, wherein each of thelongitudinal walls of the plurality of spreading devices have a formwhich is a truncated isosceles triangle and joins correspondinglongitudinal internal walls of the ejection nozzle to join togethertherewith as a continuous component.
 9. The device according to claim 2,wherein the ejection nozzle has an inlet cross-section, and wherein eachof the plurality of spreading devices has an inlet cross-section whichis one of circular or rectangular and an outlet cross-section which isan elongate rectangle and which fits at least part of the inletcross-section of the ejection nozzle.
 10. The device according to claim1, wherein the support means defines a plane of movement, wherein thehot glass substrate moves along the path in the plane of movementdefined by the support means, and wherein the longitudinal internalwalls of the slot form, with the plane of movement of the hot glasssubstrate, an angle ranging between 20° and 40°.
 11. The deviceaccording to claim 1, wherein the slot is integral with the ejectionnozzle.
 12. The device according to claim 1, wherein the support meansdefines a plane of movement, wherein the hot glass substrate moves alongthe path in the plane of movement defined by the support means, andwherein the ejection nozzle has an axial plane which is substantiallyperpendicular to the plane of movement of the hot glass substrate. 13.The device according to claim 1, wherein the device further comprisesfixed guide beams, and a bogie which supports the device and which has aplurality of rollers, and wherein the plurality of rollers engagerespective fixed guide beams and thereby enable movement of the device.14. The device according to claim 13, wherein the plurality of rollersincludes at least one U-shaped roller which engages a first fixed guidebeam and at least one cylindrical roller adapted to engage a secondfixed guide beam.
 15. The device according to claim 1, furthercomprising means for trapping stray deposits in the coating chamber. 16.The device according to claim 1, further comprising means to adjust theheight of the coating chamber above the hot glass substrate.
 17. Themethod according to claim 3, wherein the angle of convergence of the gasflow ranges, at any point along its path inside the ejection nozzle,from 4° to 9°.
 18. The method according to claim 3, wherein the gaseousmedium is supplied to the ejection nozzle via a delivery pipe having anoutlet cross-section, wherein the gas flow flows along a delivery pathwhich includes the outlet cross-section of the delivery pipe and whichincludes the ejection nozzle and the slot, and wherein the gas flowalong the delivery path has an angle of divergence which ranges, at anypoint on the delivery path, from 0° to 14°.
 19. The method according toclaim 18, wherein the angle of divergence ranges from 0° to 9°.
 20. Thedevice according to claim 1, wherein the continuous convergent path hasan angle of convergence (α) which ranges from 4° to 9° at any point.